This application relates to and claims priority from Japanese Patent Application No. 11-234271 filed on Aug. 20, 1999, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to heat exchangers, and particularly to a double heat exchanger having plural heat exchangers such as a radiator and a condenser for a vehicle air conditioner. The present invention is suitably applied for a hybrid vehicle driven switchably by an engine and an electric motor, or driven mainly by the motor while using the engine for generation of electricity.
2. Related Art
Conventionally, a hybrid vehicle has an engine and an electric motor, and needs to cool the engine and electronic parts of the vehicle such as an inverter which controls the motor. Generally, engine coolant for cooling the engine is cooled by a radiator to have a temperature of 100-110xc2x0 C. and lower. When the electronic parts are cooled by coolant, the coolant (hereinafter referred to as electronic-parts coolant) needs to be cooled by the radiator to have a temperature lower than that of engine coolant such as 60-70xc2x0 C. and lower.
In a vehicle air conditioner having a refrigeration cycle, a maximum temperature of refrigerant is approximately 80-90xc2x0 C., which is lower than that of engine coolant. Therefore, a condenser of the refrigeration cycle which condenses high pressure refrigerant in the cycle is disposed at an upstream air side of the radiator. A difference between a temperature of air having passed through the condenser and a temperature of electronic-parts coolant flowing into the radiator is smaller than a difference between a temperature of air having passed through the condenser and a temperature of engine coolant flowing into the radiator. Therefore, when electronic-parts coolant flowing through the radiator is heat-exchanged with air having passed through the condenser, electronic-parts coolant may be insufficiently cooled. As a result, the electronic parts may be insufficiently cooled by electronic-parts coolant. The electronic parts may be sufficiently cooled when an area of radiation of the radiator which cools electronic-parts coolant is increased. In such a case, however, a size of the radiator is increased.
In view of the foregoing problems, it is an object of the present invention to provide a heat exchanger which sufficiently cools a heat releasing member without increasing a size of the heat exchanger.
According to the present invention, a heat exchanger has first, second and third heat exchangers and is connected to first and second heat releasing members. The first heat exchanger performs heat exchange between a first fluid flowing through the first heat exchanger and air passing through the first heat exchanger to cool the first fluid. The first fluid cooled by the first heat exchanger is introduced into the first heat releasing member. The second heat exchanger performs heat exchange between the first fluid flowing through the second heat exchanger and air passing through the second heat exchanger to cool the first fluid to a temperature lower than that of the first fluid introduced into the first heat releasing member. The second heat exchanger discharges the first fluid cooled by the second heat exchanger toward the second heat releasing member. The third heat exchanger is disposed at an upstream air side of the first and second heat exchangers to perform heat exchange between a second fluid flowing through the third heat exchanger and air passing through the third heat exchanger. The second fluid has a temperature lower than that of the first fluid flowing through the first and second heat exchangers. At least a part of the second heat exchanger is disposed opposite a portion of the third heat exchanger which accommodates a downstream flow of the second fluid, so that air having passed through the portion of the third heat exchanger passes through the second heat exchanger.
When the third heat exchanger is a condenser, the second fluid has a lower temperature at a downstream side than at an upstream side in the third heat exchanger. Therefore, air having passed through the portion of the third heat exchanger which accommodates the downstream flow of the second fluid has a temperature lower than that of air having passed through the other portion of the third heat exchanger. As a result, a difference between a temperature of air passing through the second heat exchanger and a temperature of the first fluid flowing through the second heat exchanger is increased. Therefore, the first fluid flowing through the second heat exchanger is sufficiently cooled, and the second heat releasing member is sufficiently cooled by the first fluid without increasing a size of the second heat exchanger.
Preferably, the third heat exchanger has a condenser core which condenses a refrigerant of a refrigeration cycle and a cooler which cools the refrigerant discharged from the condenser core. At least a part of the second heat exchanger is disposed opposite the cooler so that air having passed through the cooler passes through the second heat exchanger. Since an amount of heat radiated from the cooler is smaller than that of the condenser core, a difference between a temperature of air passing through the second heat exchanger and a temperature of the first fluid flowing through the second heat exchanger is increased. As a result, the first fluid flowing through the second heat exchanger is sufficiently cooled.